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An important feature of communication between the central nervous system and the pituitary-ovarian axis is the pattern of pulsatile discharge of hypothalamic luteinizing hormone releasing hormone (LHRH). The discharge of LHRH is under control of noradrenergic, dopaminergic, and serotoninergic systems of the brain. These systems intervene between external and internal signals (e.g. photoperiod and gonadal steroids) and LHRH output. In the ewe, noradrenaline, dopamine and serotonin of the brain are implicated in the control of LHRH output, and hence luteinizing hormone (LH) release, during both the anoestrous and breeding seasons. These amines are involved in steroid-dependent and steroid-independent regulation of LHRH/LH discharge. An interplay of inhibitory versus excitatory influences of these amines on LHRH/LH release appears to govern the pattern of LHRH/LH output during the annual reproductive cycle and the ovulatory cycle. A concise overview of this topic will be provided.

The relationships between the release of LHRH, beta-endorphin (beta-END) and noradrenaline (NA) from the hypothalamic infundibular nuclei/median eminence (NI/ME) during the periovulatory period in the ewe was studied. Neurohormone release was assayed in perfusates collected from the NI/ME via push-pull cannulae. LHRH concentrations in perfusates ranged from below detectable values (5 pg) to 50 pg and from 15 to 240 pg/20 min perfusate on the days of proestrus and estrus, respectively. beta-END concentrations in perfusates ranged from 320 to 6,000 pg on the day of proestrus and fell to a range between 100 and 380 pg/20 min perfusate on the day of estrus. The NA content of perfusates ranged from an undetectable level to 0.9 x 10(4) pg/perfusate during proestrus, and rose from 1.0 x 10(4) to 6.6 x 10(4) pg/perfusate shortly before the preovulatory release of LHRH and LH. On the basis of the present observations, the following sequence of events leading to the massive LH ovulatory surge in the sheep is suggested: (1) increased secretion of beta-END in the NI/ME on the day of proestrus generates an increase in the releasable pool of LHRH through inhibition of LHRH release; (2) on the day of estrus a decreased release of beta-END allows the expression of NA activity in the NI/ME and the augmentation of NA tone facilitates the release of newly accumulated LHRH; (3) the resultant intensified LHRH output with its significantly changing pattern of release triggers the preovulatory surge of LH.

Activity of noradrenergic neurons of medial-basal hypothalamus of female rabbits in some stages of reproduction. Acta Physiol. Pol., 1978, 29 (2): 111--115. The differences were found in the activity of noradrenergic neurons of medial-basal hypothalmus (MBH) estimated by the analysis of metabolism of intraventricularly infused 3H-noradrenaline (3H-NA) in various stages of reproduction in female rabbits. The gonadal hormones and especially 17beta-estradiol seem to be involved in this activity. The rapid disappearance of 3H-NA from MBH, found immediately after mating, implicates an involvement of noradrenaline in the process of Gn-RHs release form the rabbit hypothalamus.

It has been postulated that stress induces discorrelations of the hypothalamo-pituitary and pituitary gonadal axis. In our experiments on the effect of stress on the reproductive physiology in rats and sheep we applied mild electrical footshocking of short or prolonged duration. Foot-shocking applied with some breaks during 9 h within one a day (15th day of the oestrous cycle) induced in ewes acceleration of the release of LH. Prolonged footshocking applied with some breaks during 3 days in cycling sheep caused disturbances in the circadian rhythm of the cortisol secretion, disturbances in the release of LH and led to the blockade of ovulation. Disturbances in the course of oestrous cycle occurred not only during the current cycle but also during two subsequent cycles. Rats exposed to relatively long-term stressful situation (24 h) during dioestrous displayed marked changes in the length of this phase in three subsequent post-stress oestrous cycles. To follow the neurohormonal background of the stress-induced disturbances in LH release and in the course of oestrous cycle in sheep the concentrations of beta-endorphin (beta-END) in the infundibular and paraventricular nuclei as well as in the pituitary gland under physiological and stress conditions were determined, while in rats the metabolism of brain serotonin was investigated. Footshocking in rats induced significant decrease in 5-HT concentrations in the fronto-parietal brain cortex, hippocampus, striatum, medial basal hypothalamus and the preoptic-anterior hypothalamic area. These results allow to suggest that the decline in brain 5-HT under stress conditions has some associations with the impairments in the course of oestrous cycle. Measurements of the beta-END in perfusates of medial basal hypothalamus (nucl. infundibularis) in sheep evidenced significant increase of this opioid under stress conditions and it was postulated that this increase might be the main cause of the stress-induced impairments in the course of oestrous cycle and inhibition of LH-release. In addition, it was found that beta-END suppressed the secretion of cortisol and attenuated some noxious consequences of general nature for organism.

Serotonin content in the anterior hypothalamic area (AHA) and medial basal (MBH) hypothalamus has been estimated (by the spectrofluorometric method) throughout the course of estrous cycle in the female rats. Serotonin content has been found to decrease significantly on the day of early and late proestrous in AHA and MBH, respectively. The involvement of serotonin in the process of regulation of gonadotropin releasing hormone(s) release on the level of AHA and MBH is discussed.

Noradrenaline turnover rate in the mediobasal and anterior hypothalamus of the rabbit. Acta Physiol. Pol., 1977, 28 (1): 39-43. The rate of noradrenaline (NA) turnover in mediobasal hypothalamus (MBH) and anterior hypothalamus (AH) of the rabbit was estimated by steady-state isotopic method with a tritiated noradrenaline (3H-NA) as a tracer. The disappearance rate of 3H-NA both in MBH and in AH was found to be biphasic; the first rapid phase of the NA half-life of about 30 min, followed by the second phase of slower decay of the half-life of 2.4 h and 10 h for MBH and AH respectively. The results suggest an existence of more than one metabolic pool of endogenous noradrenaline in MBH and AH and indicate regional difference in the metabolism of NA stores in the hypothalamus.